教學方

Dr. Barbara Oakley

Dr. Terrence Sejnowski

Francis Crick Professor at the Salk Institute for Biological Studies

M.S. Orlando Trejo

Assistant Professor

腳本

[MUSIC] For a long time, emotions were considered unreliable compared with cognition. This has all changed in the last few decades. Emotions are important for social interactions, learning, and decision making. Emotions are complex brain states, associated with positive and negative experiences, and they are accompanied by facial expressions. Darwin wrote a book about visual expression as a form of communication that is important for survival, and natural selection. Paul Ekman is the world's leading expert on facial expression. He was the real world inspiration for Cal Lightman in the TV drama series Lie to me, although Paul is lot nicer person than Cal. Ekman went to Papua New Guinea to find out if pre-industrial cultures responded emotionally with the same facial expressions that we do. He found six universal expressions of emotion in all human societies that he studied. Happiness, sadness, anger, surprise, fear, and disgust. Emotions are typically slow in onset and can last for a long time. Can you remember the last time that you got angry? How long did the angry mood last? There are groups of neurons very deep in the brain stem called neuromodulatory systems that control your levels of arousal, motivation, and attention. Last week, we saw that one of them, the serotonin system, was important for regulating social interactions. Another brain stem system that fans out over wide regions of the brain, uses a chemical called noradrenaline. Edronax is a drug that works along the lines of Prozac, except that it is a reuptake inhibitor for noradrenaline, and it increases its activity. It could be more effective than Prozac in helping patients who are depressed and lack the capacity for sustained motivation. Whereas, serotonin activation results in serenity and mellowness, noradrenaline activity is involved in increasing drive motivation. When a closely related molecule manufactured in your adrenal gland, called adrenaline, is released in your blood, it makes your heart pound faster and prepares your body for vigorous physical activity, paralleling the increase in mental activity triggered by noradrenaline inside the brain. Is depression caused by imbalances in serotonin or in noradrenaline? These ancient neural systems interact with one another like players in an orchestra. So part of a serotonergic drug's efficacy, may be indirect by altering levels of noradrenaline. This interaction complicates the search for effective treatments for mental disorders, and reminds us, that although we talk about this or that chemical system, brain systems are deeply integrated. There is another powerful motivational system in the brain that uses dopamine, and is centered in the few groups of cells in the midbrain. This system of dopamine neurons underlies both the motivational and the emotional facets of extraversion. High dopamine levels puts people in a good mood, energizes some people to seek out new worlds, and to go boldly where no one has gone before. But not too high a level since that leads to Tourette Syndrome, characterized by uncontrolled ballistic movements, and a blue streak of swear words, which you can imagine on your own. Your dopamine neurons can be interrogated when you need to make a decision. What should I order from the menu? You imagine each item, and your dopamine cells provide an estimate of the expected reward. Should I marry this person? Your dopamine cells will give you a gut opinion that is more trustworthy than reasoning. Problems with many incommensurate dimensions are the most difficult to decide. For example, how do you trade off a sense of humor, a good dimension, with being messy, a bad dimension? Or hundreds of other comparisons. Your reward systems reduces all these dimensions down to a common currency, the transient dopamine signal. Dopamine is a central part of reinforcement learning, which occurs when you associate a sensory input with a reward. Such as Pavlov's dog, in which food odors are are associated with salivation. Dopamine is released in the brain when an unexpected reward occurs, and dopamine levels are reduced from baseline, when an expected reward is not received. Dopamine neurons receive inputs from a part of the brain called the basal ganglia, which evaluates cortical states and assigns value to them, and is involved with learning sequences of motor actions to achieve a goal. Although this form of learning might seem simple, it has now been shown that reinforcement learning is the basis for the most powerful artificial intelligence system ever created. It is not just your cognitive systems, but also the impetus provided by your emotional systems that make you intelligent. Go is an ancient game that is highly popular in Asia. The 19 by 19 Go board is much larger than the 8 by 8 chessboard, which makes it possible to have several battles raging in different parts of the board, white against black pieces, vying for territory. Go is to chess in difficult, as chess is to checkers. If chess is a battle, Go is a war. It has been thought that Go was so difficult that no computer program could ever play at championship level. However, this changed when the Korean Go world champion played a match with AlphaGo, a program based on reinforcement learning that played itself many millions of times. It came as a shock to many when AlphaGo won the first three games, winning the match, and exhibiting in an unexpectedly high level of play. The three neuromodulatory systems based on serotonin, noradrenaline, and dopamine interact strongly with the emotional systems in the brain. Without them, we would not be human. With them, we are able to form social bonds, evaluate dangerous situations, and learn new skills. I often wondered why Spock, on Star Trek, had such a flat affect. Could it be his neuromodulators were low? Think about it. [MUSIC]